The laboratory maintenance of successive generations of Schistosoma haematobium in the hamster will be compared with maintenance in the chimpanzee. Since the chimpanzee is the closest species to man, phylogenetically,it is hoped that this nonhuman primate will be shown to be an effective maintenance host and that a well-characterized, more "natural" host-parasite system can be provided for future laboratory research. To develop the strain, a parasite species and a snail host from the same geographical region, hopefully Iran, will be used. Standard techniques will be used for passaging the parasites. To date, the difficulties in propagating human-derived S. haematobium in the laboratory have been attributed to susceptibility, or lack of it, in the snail host; however, it may be that maintenance in an aberrant (distant from man) primary host (the hamster) has brought about changes in the "infectivity potential" of the parasite, particularly during the miracidial stage. Therefore, the larval stages, particularly the miracidium, will be examined to try to determine any factors which may influence the infectivity potential.